8.2 Measuring Earthquakes
8.2 Measuring Earthquakes Earthquake Waves 8.2 Measuring Earthquakes Seismographs are instruments that record earthquake waves. Seismograms are paper records of recorded ground motion made by seismographs.
Seismograph http://www.youtube.com/watch?v=DX5VXGmdnAg
Seismogram Fastest waves Slowest waves and most destructive
8.2 Measuring Earthquakes http://www.jclahr.com/science/earth_science/tabletop/pslnkmv.html# 3 kinds of waves • P waves - Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel - Travel through solids, liquids, and gases - Have the greatest velocity of all earthquake waves “P waves move through the entire earth- crust, mantle, and core) like a slinky”
8.2 Measuring Earthquakes Earthquake Waves 8.2 Measuring Earthquakes • S waves Seismic waves that travel along Earth’s outer layer - Shake particles at right angles to the direction that they travel - Travel only through solids - Slower velocity than P waves “S waves move through the ground like a rope”
Seismic Waves Paths Through the Earth
8.2 Measuring Earthquakes Locating an Earthquake How far is your location from the epicenter? 8.2 Measuring Earthquakes • Distance from you to epicenter is found by the measuring difference in the arrival times between P and S waves.
Locating an Earthquake 3 seismographs are required to correctly locate the epicenter of an earthquake Epicenter is located where three circles intersect
8.2 Measuring Earthquakes Momentum Magnitude • Moment magnitude is the most widely used measurement for earthquakes Estimates the energy released by earthquakes. • Measures very large earthquakes
Earthquake Magnitudes
Some Notable Earthquakes
Modern Earthquakes 7.2 Turkey in 2011 572 deaths 9.0 Japan in 2011 18000 deaths http://www.youtube.com/watch?v=fraPBV4kzvI